1. Technical Field
The present invention relates to a zinc-plated steel sheet for hot press forming and more particularly, to a zinc-plated steel sheet for hot pressing having excellent surface characteristics able to secure a stable plating layer by preventing deterioration of the plating layer during hot press forming, a hot-pressed part using the same, and a method of manufacturing thereof.
2. Background Art
Recently, demand for high-strength steel sheets for the purpose of improving vehicle fuel economy to meet with environmental protection regulations has rapidly increased. In accordance with the strengthening of automotive steel sheets, wear and fracturing may occur during press forming, and the formation of complex-shaped products may be difficult. Therefore, in order to resolve such limitations, the production of products by hot pressing, in which a steel sheet is heated to be molded in a hot state, has greatly increased.
A steel sheet for hot pressing is generally subjected to hot press forming in a temperature range of 800° C. to 900° C., and a surface of the steel sheet may be oxidized, thereby generating scaling. Therefore, a separate process for removing scaling after product formation, such as shot blasting, is required, such that product corrosion resistance may also be inferior to that of a plated material.
Therefore, in order to address such limitations, products as that of U.S. Pat. No. 6,296,805, in which aluminum (Al)-based plating is performed on a steel sheet surface to maintain a plating layer, while formation of an oxidation reaction of the steel sheet surface in a heating furnace is prevented and corrosion resistance is increased through the formation of a passive Al film, have been developed and commercialized.
However, with respect to the Al-plated material, heat resistance at high temperatures is excellent, while corrosion resistance may be inferior to that of a zinc (Zn)-plated steel sheet formed through a sacrificial anode method and manufacturing costs may also increase.
Since Zn high-temperature heat resistance is significantly inferior to that of Al, a plating layer of a Zn-plated steel sheet manufactured via a typical manufacturing method may be non-uniformly formed due to alloying of a Zn layer and high-temperature oxidation in a high temperature range of 800° C. to 900° C., and a ratio of Zn in the plating layer may be decreased to less than 30%. Therefore, its functionality as a plating material may be reduced in terms of corrosion resistance.